The long-term objective of the proposed research program is to elucidate further the mechanisms of functional recovery after injury to the adult mammalian spinal cord. Terminal axon sprouting of severed nerve fibers and collateral axon sprouting of intact fibers adjacent to the denervated fields of the damaged fibers have been identified in the mammalian spinal cord after injury. Anatomical studies of the spinal cord after injury have demonstrated the formation of new synaptic structures. However, little is known about the functional correlates of this anatomical evidence of central regeneration. More specifically, it has not been determined whether the injured adult spinal cord has the capacity for making new functional synaptic connections. The immediate aim of the proposed research is to vacate synaptic sites on spinal motoneurons and to test whether new group la afferent synaptic terminals "functionally" occupy these vacated sites. The approach of this laboratory to this problem is primarily electrophysiological, utilizing intracellular recording and stimulation and spike-triggered averaging techniques. The formation of such new functional synaptic connections would be indicated by increased amplitude, increased connectivity, and alterations in the shape indices of group la single fiber EPSPs. The interpretation of this electrophysiological data will be further strengthened by direct anatomical studies of the sprouting of group la afferent fibers under identical experimental conditions using recently developed techniques. These studies will certainly provide important evidence concerning the "functional" regeneration capacity of the mammalian spinal cord after injury. Additional aims are to understand the acute and chronic increased excitability of surviving neuronal elements after denervation and injury.